Although recent reports of Pope John Paul II's medical condition have focused on a series of seemingly separate ailments, doctors say his downward spiral likely stems from a larger problem - his long struggle with Parkinson's disease.
In the past month, the 84-year-old Pontiff has suffered from breathing, swallowing and speech problems. He has had a breathing tube installed in his windpipe and a feeding tube passed through his nose into his stomach. He speech became so labored he managed to emit only a rasp while blessing pilgrims, then he was unable to speak at all.
Doctors say such problems are common among those in the advanced stages of Parkinson's, progressive disease that destroys nerves controlling movement.
"The chances are overall that this is the natural history of Parkinson's," said Dr. Hassan Makhzoumi, director of pulmonary medicine at St. Joseph Medical Center.
Initially, Parkinson's causes a slow and shaky gait, stiff limbs, tremors and a loss of facial expression - problems painfully visible to people who have observed the pope since the illness set in over a decade ago.
But as the disease worsens, it cripples the fine muscles in the throat that control swallowing. Food that should pass smoothly through the esophagus and into the stomach can spill into the windpipe, triggering recurrent respiratory infections that can make it hard to breathe. Saliva and stomach secretions can enter the lungs, too.
Dr. Paul Fishman, a Parkinson's specialist at the University of Maryland School of Medicine and the Baltimore Veterans Affairs Medical Center, said pneumonia is the most common cause of death in Parkinson's patients.
"When people die of Parkinson's, they are dying of pneumonia, and they are dying of pneumonia because their own secretions are going into the lungs," Fishman said.
Though flu was the reason the Vatican gave for the respiratory problems that made the breathing tube necessary, Fishman said influenza often triggers pneumonia in the elderly.
"Remember, these patients don't clear respiratory infections well. They don't breathe very well. They have severe rigidity of the chest. It's not like they can take a deep breath and cough it out, the way we clear our own secretions."
Dr. Michele Bellantoni, medical director of the Johns Hopkins Bayview Care Center, said a simple way to think about the pope's condition is that he is suffering the medical complications of frailty.
"His longstanding Parkinson's has made him very frail," she said. "With frailty comes a higher risk of infection and then more debility and more problems. It's a vicious spiral."
Faced with such problems, doctors might insert breathing and feeding tubes to keep the handling of food and air separate when the throat muscles are no longer able to do so.
"It's clear that Pope John Paul was at that stage, which is why he had the tracheostomy done and why he had the feeding tube," said Makhzoumi of St. Joseph. "Unfortunately, none of this is foolproof, and ultimately these patients succumb to pneumonia."
Urinary tract infections, the latest problem to strike the pope, aren't as common among Parkinson's patients, doctors said. Some said the ailment might be coincidental, though Fishman said patients treated with antibiotics for various problems might develop drug-resistant infections elsewhere.
The nasal feeding tube given to the Pope is usually a short-term solution to feeding problems, doctors said. Patients find it irritating and ultimately feel better with a tube inserted directly through the skin into the stomach. If the pope survives the next few days, he may have to decide whether to have that kind of tube surgically placed, doctors said.
Commenting on the Terri Schiavo case, the pope has said that he does not consider the provision of food and water to be an extraordinary measure in prolonging life.
Sun staff writer Michael Stroh contributed to this article.